Voltage amplifier



- Sept. 13, 1927.

T. E. SHEA VOLTAGE AMPLIFIER 2 Sheets-Sheep J,

five/War.- 77/770Ihyf, Shea i Filed Oct. 18, 1925 S t. I

ep 1.927 T. E. SHEA VOLTAGE AMPLIFIER Filed 001' 18, 1923 2 Sheets-Sheet2 Hya.

:4 Frequency in Kilocycles hve/vfah' 7/77? by X of/zy f. Jhed in itselectrical action a Patented Sept. 13, 1927.

UNITED STATES 1,642,389 PATENT OFFICE.

TIIOTHY E. SHEA, OF RUTHERFORD, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRICCOMPANY, INCORPORATED, or vnew YORK,

N. Y., A CORPORATION OF NEW YORK.

VOLTAGE AMPLIFIER.

Application fled October 18, 1923. Serial No. 669,219.

This invention relates to the production of high voltages of certainselected frequencies by means of uniform or artificial resonating lines.Artificial lines ma be defined as recurrent series of identica sectionseach section having lumped impedance eflfectively in series with theline and lumped admittance effectively in shunt across the line.

Such an artificial line tends to simulate uniform line of distributedconstants, the total series impedance of the uniform line being equaltothe total series impedance of the artificial line and the total shuntadmittance of the uniform line being equal to the total shunt admittanceof the artificial line at all frequencies. The electrical anglesubtended by a uniform line of distributed constants is hyperbolicradians where Z and Y are the total series impedance and the total shuntadmittance of the line. The correction factor which must be applied tothe electrical angle of a uniform l1ne in order to obtain the electricalangle subtended by the artificial line is:

2m where m is the number of recurrent sections in the artificial line.For the derivation of this expression reference is made to Kennelly,Artificial Electric Lines, copyright 1917, and particularly to EquationNo. 244, Chapter VI. Y

When a voltage is applied through a very small impedance at one. end ofa uniform line the voltage produced atthe remote end, if the remote endis terminated in an infinite impedance will be V,=V sech 6 (3) theapplied voltage and V is the voltage at the remote end. The relationshipexpressed by Equation 3 is well known, (see for example Fleming, thePropagation of Electric Currents in Telephone and Telegraph Conductors,Chapter III, Equation 34) and in its derivation it is customary toassume that the Whole E. M. F. of the source is applied to the lineterminals regardless of the current strength. In other where V, is

the line, and may be made of the 9 (n being any odd integer) the voltageat the far end of the line will be very large with respect to theapplied voltage. There thus results a large voltage amplification whichwill be limited only by the efiective resistance and conductance of theline but if these are reasonably small the amplification may be madelarge.

The artificial line will simulate a smooth line in producing suchvoltage amplifications except that the calculated frequencies at whichthe voltage amplifications occur must be corrected by applying to theelectrical angle of the smooth line the correction factor given inEquation r The correction factor may be controlled by m, the number ofrecurrent sections in order dethe proper number of secsired by usingtions.

In order that in either uniform or sectional lines it is necessary thatin certain frequency ranges the series impedance be substantiallyinductive reactance and the shunt admittance be substantiallycapacitative susceptance, or vice versa, that the series impedance besubstantially capacitative reactance and the shunt admittance besubstantially inductive susceptance. The angle subtended by the smoothline and the artificial line will then be respectively where X is thetotal series reactance and 13 the total shunt susceptance, and

Heretofore, so far as known, no use has been made of voltages producedat the distant end of a uniform or sectional artificial line because (1)the power output is small, (2) the introduction of the impedance ofordinary translating circuits, to which the voltages would ,have to betransferred,

quencies by means of causes the disappearance of the resonance phenomenathemselves, and (3) the impedance of the voltage source has not beenproperly designed and related to the line. In particular it may bepointed out that in the prior practical application of sectionalnetworks, of thetype under discussion as filters, it has been the usualcustom to terminate the network in an impedance equal to the surgeimpedance of the network. Because of this the phenomenon of high voltageproduction at certain selected frequencies is avoided.

It is herein proposed to utilize the high voltages which ma be set up bythe methods hereinbefore described by employing them to control vacuumtube repeater circuits of practically infinite input impedance and sincesuch circuits are controlled almost entirely by voltage variationsrather than power variations it becomes possible to utihas what haveheretofore been considered negligibly small amounts of power. It isknown how to make vacuum tube input circuits of impedances of the orderof 1,000,000 ohms and upward for almost any frequency over a wide rangeof frequencies. These values are suiiiciently high to be consideredpracticall infinite inasmuch as they disturb, to a neg igible extentonly, the resonance phenomena herein considered. Lower impedances may bemade use of under certain conditions consequently the invention is notlimited to any precise value of input impedance.

The impedance of the input circuit or voltage source through whichvoltages to be amplified are applied to the network may be made to havenegligible efiect.

(1) By making the impedance of the portion of the circuit through whichthe voltages are impressed on the network, small in comparison with theimpedance of the network,

(2) By incorporating the impedance of the voltage-providing circuit inthe structure of the line,

(3) By the insertion of an annullin impedance in series with the voltageproviding circuit, or

(at) By translating the voltages to be' areplified through a circuit sodesigned that its ougput impedance may be treated by (1),

9. or 3 An tibject of the invention, therefore, broadly stated, is toproduce greatly amplifled voltages of a selected frequency or reuniformelectrical lines or artificial lines.

In further describing the invention reference will be made to theaccompanying drawings wherein Fig. 1 is a diagram of a uniform linewhich is used in explaining the theory of the invention; Fig. 2 is adiagram illustrating the selectivity of such a line as Fig. 1 forcertain voltages; Figs. 3 and 4 are diagrams of a T-network or line anda inetwork or line respectively; Figs. 5 an 6 are diagrams of typicalsectional lines with formula applicable to the design thereof; Figs. 5,5", 6 and 6 are graphs explanatory of Figs. 5 and 6; Fig. 7 is a circuitdiagram of a system for producing a selected series of carrier Waves;Fig. 7 a modified form of Fig. 7 and Fig. 8 a diagram illustrating theselective action of such a circuit as"that of Fig.7.

A consideration of the general theory of this invention and of theeffect of series resistance and shunt conductance upon the voltageswhich will be set up at the distant end of the line will make clear thebasic principles of operation of systems embodying the invention.

With reference to Fig. 1 the uniform line 10 has a series impedance forunit length 11 of Z :7'+ jwL ohms or a total series impedance of where Zis the length of sistance per unit length, L is the inductance per unitlength, R is the total resistance, and L is the total inductance. Theshunt admittance per unit length 11 is Yzg-l-joG or a total shuntadmittance of where g is the shunt conductance per unit length, C is theshunt capacity per unit length, and G and C. are the total shuntconductance and capacity respectively.

A source of voltage 12 of value c is con nected across the inputterminals BE and a vacuum tube repeater across the output terminals DF.We will assume that the gridfilarnent im edance of the repeater is onlynegligibly t itierent from infinity.

Then

the line 1' is the relln'm z. 1 secht) (6) T representing the ratio ofvoltage, V at the "far end of the line to the voltage, Vnfq, impressedupon the near or input end.

=sech w (53%; 1), (8)

where 9, and 8,, are the real and the imaginary parts of 9. Further,

emi..=. a=a.+ie.=

' sponds to an where a=th6 electrical angle per unit length of the line,and a, and 11 are the real and imaginary parts of a If wJm=%- n beingany odd integer, then i n1! 1 1 .1211 T-Sh[;*(-Q;+'Q;) 4']approximately. ut since sech (9 +jng)= Fjcsch 6, the size of T isapproximately determined by 21 i T-csch 4 (11) But since each 6approaches when 6 is small we have approximately,

From the foregoing it appears that for large values of Q and Q,, Tbecomes very great.

The behavior of T for large values of Q- and Q. for a line such asshownin Fig. 1, is shown in Fig. 2 in which the ratio T for each peak valueof voltage has a definite finite value given by Equation (12). Tilt andG are constant the several peaks will be of equal amplitude. If Q and Qare constant the successive peak voltages will diminish in a ratioinversely proportional to the frequency.

Consider the action of artificial lines having lumped shunt impedancesand lumped series impedances such as'shown in Figs. 3 or 4, these being"representative of symmetrical lines having the two generally used typesof termination commonly known as mid-series and mid-shunt terminations.

The electrical angle a of such lines per section is where Z is theseries impedance and Y is the shunt admittance of each section.

For a line having m sections angle factor is electrical,

in which 9' and 6' are the real and imaginary parts respectively of 9.

If. Z be and jwL, and Y condensive, having components g and jmC,

=2m sinh' ur lljg H06 1) (16) and ' 1 T=sech 2m smh w /LO +31) 1) (17)By comparing Equation (17 with Equation 8) we see that these twoequations are identical if it be assumedthat The approximation inEquation (18) holds when 9 does not exceed .5 to 1.0 radians from whichit follows that the number of sections should be chosen so that thehighest of the desired resonance frequencies correangle of less than oneradian per section. Formula (12), therefore holds true within certainlimits for inductive-condensive lumped lines such as shown in Figs. 3and & wherein Z and Z are in the form of inductance .and capacity,respectively, and the correction factor of Equation (2) may be employedwhere the disparity is appreciable to determine the actual frequenciesof resonance." v

The foregoing mathematical analysis shows that voltages of certainfrequencies may be greatly. amplified by means of uniform or sectionallines.

- \Vith uniform lines the maximum amplifications will occur atfrequencies harmonical ly related.

Lines of lumped constants may be designed so that the frequencies ofmaximum amplification are in approximately harmonic relationship througha considerable range.

inductive, having components 1' The frequencies may depart from harmonicrelationship if the design is appro priate for such departure. Althoughthe principal emphasis in this specification is laid upon amplificationof voltages of harmonically or nearly harmonically related frequenciesit is contemplated that the principles herein set forth may be appliedin designing modified arran ements to select and amplify voltages ofrequencies in a great variety of relations.

In Fig. 5 is shown a typical line 20 adapted, in accordance with thepresent invention, to select and amplify certain odd harmonic voltages.The line comprises lumped series inductances L and lumped shuntcapacities C Under Fig. 5 are given the formula: applical le to the line20. In Figs. 5 and 5" are graphs of the quantities 9, Z and Y and agraph indicating the resonance frequencies which comprise a fundamentaland an indefinitely extended series of odd multiples thereof.

In Fig. 6 is shown another typical line 21 in which the lumped seriesinductance of adjacent sections have a mutual series aiding inductanceM. The formulm applicable to this line are shown in Fig. 6 and in Figs.'6 and 6 are graphs of the quantities 9, Z and Y and a graphindicating-the selected frequencies. In connection with the graph ofselected frequencies it is noted that the ratio controls the asymptoticlimit of 9'.

In theory any number of resonance frequencies from one to infinity maybe had by varying the ratio {C By reference to Figs. 7 and 8 thesolution of a'practical problem may be illustrated. Let it be requiredto produce frequencies of 1,000 cycles, 3,000 cycles, 5,000 cycles etc,for application to a carrier suppression modulator. Let it be assumedthat the source denoted by E in Fig. 7 is adapted to generate a voltagewave containing components of the desired frequencies and of suchreactance as to properly form the end section of a line 20 similar tothe line 20 of Fig. 5. A thermionic repeater 22 of very high inputi1npedance terminates the line. The output circuit of the repeater 22 iscoupled to a modulator 23 of the carrier suppression type which issupplied with oscillations of a frequency of 31,000 cycles per secondfrom a source 24 for translating the selected wave frequencies to newvalues.

Let the surge impedance of the line 20 be 1,000 chins and let it haveten sections. Neglecting resistance the iterative impedance IT Z.,= 61,000 ohms. Since H mo {L 0 n (20) For the fundamental frequency H 76 ow1 2 2 fo1 1 2 Therefore,

1 .l a /no. ,7OE 4OOOO .025 10 (21) 8o Whence L,:.025 henries.

C =.025 microfarads Now assume Q 50 and Q zinfinity, whence H I 2 T=sech9=sech /8994? -csch H 64.

The value of T for 3,000 cycles, etc., may be similarly obtained inaccordance .with the comments following equation (12). If r and g areconstant T zT and the output current of the modulator 23 Will have anamplitude varying with frequency as indicated in Fig. 8. The voltages of20, 28, 30, 32, 3% and 36 kiloeycles appear in the output circuit ingreatly amplified form and may be selected by any suitable or knownsystem of tuned circuits or other electrical networks and used, forexample, to set up carrier waves in a carrier telegraph system. It isapparent that carrier waves may thus be produced for supplying wavesconstituting (1) a full harmonic system, (2) an odd harmonic system, (3)a non-harmonic equally spaced system or 1) a non-harmonic but unequallyspaced system;

In Fig. 7 is shown a modified form of vacuum relay input circuit inwhich a high resistance 24 is connected across the gridfilament circuitin series with a source 25 for negatively polarizing the grid of therelay. The resistance 24 may have a value of the order of 1,000,000 ohmsor more which makes the input impedance a sufficiently closeapproximation to the theoretically desirable infinite impedance.

Another use of the present invention is 120 in systems of radio or otherfrequency amplification where large amplifications are difficult toattain. By making use of the present invention for greatly increasingthe voltage at a selected frequency or frequencies and applying thevoltage thus increased to an electron discharge amplifier a large stableamplification can be attained. One or more stages of a multistagerepeater may thus be replaced by a circuit in accordance with thepresent invention with advantages in selectivity and amplification.

The invention may be used in an case where frequencies which a line cane de signed to amplify are to be selected and other frequenciesattenuated or extinguished. The translating element or relayconstitutesthe high terminal impedance.

It is to be noted that the lines employed in carrying out this inventionresemble certain types of filters described for example, in CampbellPatent No. 1,227,113, May 22, 1917. The selective phenomena, however,with which the present invention deals are present both in thetransmitting and in the non-transmitting ranges of such filters asordinarily used but principally in the transmitting range. Furthermorethe terminations which such filters require and which are employed inpractice would destroy the resonance phenomena upon which this inventiondepends.

The principles and mode of application of the invention having beendescribed, the features believed to be novel are set forth in theappended claims.

What is claimed is:

. 1. A systemfor selectively amplifying a plurality of voltage wavescomprising in combination, a wave source adapted to generate a pluralityof waves of different frequencies, a space discharge amplifier includinga control electrode, and an artificial line of recurrent structurecomposed of substantially non-dissipative reactances connected betweensaid source and the control electrode and cathode of said amplifier, thereactances of said line being roportioned to produce resonances at therequencies of the waves generated by said source, and the impedance ofsaid source being negligibly small in comparison with the surgeimpedance of said line, whereby the effect of the line resonances isstrongly intensified.

2. A system for the selective transmission of Waves of harmonicallyspaced frequencies comprising in combination, a wave source adapted toproduce a plurality of waves of harmonically related frequencies, aspace discharge amplifier including a control electrode, and anartificial line of recurrent structure composed of substantiallynon-dissipative reactances connected at one end to said source and atthe other end to the control electrode of the cathode of said amplifier,each section of said line comprising an inductance in series with theline and a capacity in shunt to the line, and the impedance of said wavesource being negligibly small in comparison with the surge impedance ofsaid line, whereby the effect of the line resonances is stronglyintensified.

3. A line of recurrent sections of reactive elements having a source ofvoltage of a plurality of frequencies connected to one end and the inputterminals of a space discharge relay connected to the other end, theimpedance of said relay between its input terminals being more than onehundred times the surge impedance of the line, and the impedance of saidvoltage source being less than one hundredth part of the surge impedanceof the line.

4. A system for selectively amplifying voltages of harmonically spacedfrequencies comprising a low impedance source of harmonically relatedwaves, a space discharge amplifier, and an artificial line having aplurality of recurrent sections of reactive elements, said line beingconnected at one end to the control electrode and cathode of saidamplifier and being connected at the other end to said source, andfurther being so terminated at said source as to incorporate thereactive portion of the impedance of the wave source as an element ofthe line whereby the line is substantially short-circuited by saidsource.

In witness whereof, I hereunto subscribe .my name this-16th day ofOctober A. 1).,

TIMOTHY E. SHEA.

